With the rapid development of technology, various electronic devices have become indispensable tools in our daily lives and work. These electronic devices provide assistance in a good number of fields such as information transfer, business transaction, interpersonal communication, document preparation, and computer graphics, so as to enable better and faster completion of certain tasks. Typically, the casing of such an electronic device is provided with a push button structure which can be pressed by the user to start the electronic device or activate different functions thereof. The conventional push button structures are made by an injection molding process in which a specific amount of molten plastic is injected under high pressure into a mold and, once the molten plastic is cooled and cured, a casing with a push button structure is formed and ready to be installed on the intended electronic device.
FIG. 1 shows a push button structure 1 that is used in most of the electronic devices nowadays. The push button structure 1 includes a casing 10 and a button body 12. The casing 10 has a surface provided with an opening 101, wherein the opening 101 extends through the surface. The button body 12 is formed in the opening 101 and has an outer periphery spaced from the inner periphery of the opening 101. A straight lever 121 extending from one end of the button body 12 has one end connected to the inner periphery of the opening 101 such that the button body 12 is movably positioned within the opening 101. When the button body 12 is pressed, the lever 121 is also subjected to the pressing force. As a result, the end of the lever 121 that is adjacent to the button body 12 is deformed, allowing the button body 12 to move inward of the casing 10 and trigger an electronic switch in the electronic device. Once the pressing force is removed, the lever 121 resiliently resumes its original position and brings the button body 12 back to its original position, too. Thus, by significant displacement of the button body 12 when pressed, the electronic switch is triggered to activate or deactivate the corresponding function(s) of the electronic device. However, the push button structure 1 has the following drawbacks:
(1) Limitation in lever thickness: As the push button structure 1 depends on deformation of the lever 121 to enable movement of the button body 12 and thereby trigger the electronic switch, the lever 121 must not be too thick, or the elasticity of the lever 121 will be reduced, which prevents the deformation required for the button body 12 to be pressed against and trigger the electronic switch. In other words, an excessively thick lever 121 will lower the sensitivity of the push button structure 1. Therefore, while designing the push button structure 1, the thickness of the lever 121 must be controlled to ensure smooth operation of the push button structure 1.
(2) Limitation in lever length: Now that the lever 121 has its limitation in thickness as stated in the previous paragraph, the lever 121 must also not be too long; otherwise, when subjected to an undue pressing force, the end of the lever 121 that is adjacent to the button body 12 may bend at such a large angle (e.g., 30˜50 degrees) that the lever 121 is overloaded and breaks, thereby compromising the durability of the push button structure 1. Further, if the lever 12 is too long, the gap between the outer periphery of the button body 12 and the inner periphery of the opening 101 will be large and unsightly, and the lever 12 can be so floppy that the button body 12 is readily moved by the user's unintentional actions and thus triggers the electronic switch by accident, which is very inconvenient. In addition, if the lever 12 is too long, the button body 12 may tilt to one side when pressed and gives the user only a vague feel of its being pressed.
(3) Low yield rate: During the injection molding process of the push button structure 1, the cross section of the lever 121—which is under the aforementioned design limitations—tends to reduce the injection speed of molten plastic and therefore result in defects or a sink mark on button surface of the button body 12. In consequence, not only is the yield rate low, but also the production cost is increased.
To overcome the foregoing drawbacks, another kind of push button structure as shown in FIG. 2 was developed. The push button structure 2 in FIG. 2 includes a casing 21 and a button body 22. The casing 21 is provided with an opening 210 and a post 211 adjacent to the opening 210. The button body 22 has a hole 221 at one end and a pressing portion 223 at the other end, wherein the pressing portion 223 extends from one side of the button body 22. The other side of the button body 22 is protrudingly provided with a projection 225. The hole 221 is mounted around the post 211 and is fixed to the casing 21 at a position adjacent to the opening 210 by gluing or other fastening means. The pressing portion 223 corresponds in shape to the opening 210 and is received therein. When pressed, the pressing portion 223 is moved inward of the casing 21 about a fulcrum defined by the hole 221, thanks to elasticity of the button body 22, thus allowing the projection 225 to trigger an electronic switch 23 in the casing 21. As the button body 22 of the push button structure 2 is not integrally formed with the casing 21, the injection molding process of the button body 22 is safe from uneven injection of molten plastic. In addition, by controlling the length of the button body 22, the portion of the button body 22 where the hole 221 is formed is prevented from excessive deformation when an overly large pressing force is applied to the pressing portion 223; therefore, the durability of the button body 22 is enhanced.
The push button structure 2, though free of the injection molding problem described above, has a far higher production cost than its integrally formed counterpart because the casing 21 and the button body 22 must be made separately. Besides, although the push button structure 2 is not subject to the aforesaid limitation in thickness, there is still length limitation on the button body 22, for if the button body 22 is too short, the portion of the button body 22 where the hole 221 is located may break when deformed beyond a certain limit. Thus, the push button structure 2 still leaves much to be desired in terms of improving the conventional push button structures. Accordingly, the issue to be addressed by the present invention is to design a push button structure which is integrally formed to lower production costs, which prevents uneven injection of material in the injection molding process, and which, when pressed, gives the user a clear feel of being so.